The medical records for the population of Olmsted County, Minnesota, for the past half century can be accessed through a central file maintained at Mayo Clinic and developed through a grant from NIGMS. This has been the source of data for the most reliable estimates in the United States of incidence rates, long-term trends and survivorship of diseases of the nervous system. This index has already served as the basis for a myriad of neuroepidemiologic studies, many relating to health issues of national importance, and all with excellent case ascertainment and follow-up. The core data facility is available to all qualified investigators, both within and outside athe Mayo Clinic for use in descriptive and analytic studies in the neurosciences as well as for research on health care needs and utilization. We now seek a program project in neuroepin=demiology in order to: 1) extend a commitment to population-based epidemiologic studies of neurologic diseases; 2) continue a tradition of collaborative effort between epidemiologists and neuroscientists in the study of incidence, trend, and risk factors; and 3) maintain this unique data resource at its present level of utility. The specific aim is to continue this collaborative tradition by means of 22 descriptive and/or analytic epidemiologic projects. In addition to a systematic update and proposed comprehensive publication for the more common serious and progressive CNS disorders, new efforts will include studies on mental retardation, Meniere's disease, head and spinal cord injury, narcolepsy, anorexia nervosa, gliomas, meningiomas, and more than a dozen other topics. Methods consist of identification, retrieval and review of all pertinent medical records of local residents, as the basis for descriptive, case-control, and historical cohort analyses. Since nearly 100% of the population is registered in a medical facility included in the data network, a unique opportunity exists for unbiased control selection; the detail records and their accessability will also facilitate proposed studies of familial aggregation.